1. Field of the Invention
The present invention relates to an encoding/decoding system, or transmission/reception system for image signals, adapted to transmit/receive image information with a high degree of efficiency.
2. Prior Art
FIG. 1 is a conceptual diagram showing a receiver side of a face image transmission and receiving system according to a prior art as disclosed in Japanese Patent Public Disclosure (KOKAI) No. 162492/89. In the drawing, numeral 100 designates a codebook which stores sets of parameter values of respective mouth shape model images which show geometrical characteristics of a mouth in response to phoneme signals, numeral 101 a memory which stores mouth shape image information of pixels of the mouth part defined by the respective sets of parameter values stored in the codebook 100, and numeral 102 a combining section adapted to modify the mouth shape image information read out from the memory 101 in accordance with the parameter values from the codebook 100 and to combine it with face image information excluding the mouth shape image information of pixels of the face part received from the transmission side. Numeral 103 denotes an initializing apparatus including a normalization codebook for initializing the codebook 100 in response to the initial face image information.
FIG. 2 is a block diagram showing an image signal transmission and reception system incorporating such a receiver as shown in FIG. 1. In the drawing, numeral 112 designates a transmission side provided with an image processing section 110 and a sound encoding section 111 for generating and transmitting an encoded image and sound information S.sub.1 and S.sub.2 to a receiver side 113. In the receiver side 113, a mouth shape model transformation section 114 and a combining circuit 115 form the combination of the combining section 102 and memory 101 shown in FIG. 1. The receiver side 113 also comprises a sound decoding section 116 for decoding the encoded sound information S.sub.2 from the transmission side 112 and a sound recognition section 117 for recognizing the decoded sound signal S.sub.3 and generating a phoneme signal S.sub.4 in response to the sound signal S.sub.3.
Operation of the system shown in FIG. 2 will next be explained.
When face image information is input to the image processing section 110, it, in turn, extracts face image information S.sub.5 other than that of the mouth and transmits such information without encoding to the combining section 115 in the receiver side. On the other hand, when the sound encoding section 111 receives sound input information, it outputs the encoded sound information S.sub.2 to the sound decoding section 116 in the receiver side 113. The transmitted sound information is then decoded thereat and converted into the phoneme signal S.sub.4 corresponding to the sound input information at the sound recognition section 117.
The codebook 100 outputs a set of parameter values S.sub.7 of the mouth shape model image relative to the phoneme signal S.sub.4 output from the sound recognition section 117 to the mouth shape model transformation section 114, and then a transformed mouth shape model image information S.sub.8 dependent on the set of parameter values S.sub.7 is provided to the combining circuit 115. At the circuit 115, the face image information S.sub.5 other than the mouth shape model from the transmission side 112 and the transformed mouth shape model information S.sub.8 are synthesized to output the whole face image output S.sub.9. At the same time, the decoded sound output S.sub.3 corresponding to the mouth shape model image is output from the decoding section 116.
In the prior encoding/decoding system for the image signals explained above, since the image information of the portions of the face other than the mouth part is transmitted as raw signals, it has been difficult to transmit an image at a low bit rate.
Further, since the mouth shape model image information are all dependent on the sound encoding and decoding sections and the sound recognition section, if an error is caused in these sections, the obtained mouth shape model image will not harmonize with the original face image other than the mouth, resulting in an incongruous image.